The present invention relates to a method of determining an optimized value of brake pressure ratio between a tractor and one of a trailer and semitrailer, and, more particularly, to a method in which an increased value of the brake pressure of the trailer or semitrailer in relation to the brake pressure resulting from the position of the brake pedal is targeted for a particular duration at the beginning of a braking operation and to a method in which a brake pressure being targeted for the trailer is allocated to the brake pressure of the tractor.
A method of determining a value of the brake pressure ratio between a tractor and a trailer or semitrailer has already been disclosed in the above-mentioned application. In that disclosed method, the allocations of the brake pressures of the tractor and of the trailer or semitrailer are recorded during steady-state braking operations and stored as reference values for future braking operations. Intermediate values between these stored allocations are gained by interpolation from the stored allocations. After the reference values of the brake pressures have been set, an adjustment takes place such that the measured coupling force between the tractor and the trailer or semitrailer is adjusted to its set value. If, in turn, a steady-state braking operation is achieved by this adjustment, the allocation of the brake pressures of the tractor and the trailer or semitrailer which have then been set is, in turn, recorded and stored. Furthermore, it is disclosed in this application to carry out a pressure boost at the beginning of a braking operation by giving the trailer or semitrailer a constant value of the brake pressure which is increased in relation to steady-state values for a particular duration at the beginning of a braking operation.
An object of the invention is to determine a brake pressure ratio between a tractor and a trailer or semitrailer so as to give the greatest possible driving comfort, the least possible wear of the components and the greatest possible degree of driving safety with the least possible constructional expenditure at the same time.
This object has been achieved in a method of determining an optimized value of the brake pressure ratio between a tractor and a trailer or semitrailer according to the present invention by the increase of the brake pressure of the trailer or semitrailer taking place as a function of the brake pressure resulting from the position of the brake pedal. In braking operations when the tractor is travelling without one of the trailer and semitrailer, an allocation of achieved deceleration to the tractor brake pressure is stored as a function of a load state of the tractor, the allocation comprising the forming of a ratio of achieved deceleration to the tractor brake pressure whereby, in subsequent braking operations when the tractor is travelling with one of the trailer and semitrailer, the brake pressure is supplied for one of the trailer and semitrailer and is allocated to the tractor brake pressure such that, in the braking operations, the actual value of the deceleration at the prevailing tractor brake pressure, with regard to the current tractor load state, corresponds to the value, derived from the stored allocation, of the deceleration achieved without one of the trailer and semitrailer at the same tractor brake pressure and with the same tractor load state.
It is advantageous in the present invention that the sensing of the coupling force can be dispensed with. To simplify a description of the present invention, only the term "trailer" is used in the following text. It will be understood by one of ordinary skill that the ratios for a semitrailer result analogously.
To compensate for or at least reduce the "run-up impact" of the trailer at the beginning of a braking operation, first a relative increase of the trailer brake pressure takes place in relation to the trailer brake pressure usually resulting from the brake pressure of the tractor in order thus to compensate for the longer response time of the brake system of the trailer. In a braking operation with a large deceleration requirement, no relative increase of the trailer brake pressure takes place at the beginning of the braking operation in order to guarantee the shortest possible braking path and to ensure that no overbraking of the trailer takes place. In braking operations with a low deceleration requirement, no problems arise in respect of driving stability (lateral guiding, traction) due to a certain overbraking of the trailer at the beginning of a braking operation. On the contrary, clear improvements result in respect of comfort and economy.
Furthermore, in braking operations, control of the brake pressure of the trailer can be implemented so as to give an optimized coordination of the brake force distribution between the tractor and the trailer. This can take place in a manner according to the present invention in that the deceleration of the tractor resulting from a particular brake pressure is stored as a function of the respective load state (loading) when the tractor travels without a trailer. When travelling with a trailer, a brake pressure is then supplied for the trailer such that, under the prevailing load state of the tractor corresponding to the prevailing brake pressure, a deceleration is set which corresponds to the stored value of the tractor deceleration without a trailer under the same load state and the same brake pressure. It is thus guaranteed that, on one hand, the brakes of the tractor do not have to perform braking work which arises due to the additional load of the trailer, thereby avoiding overbraking of the tractor, and that, on the other hand, the brakes of the trailer do not have to perform braking work which arises due to the load of the tractor, thereby avoiding overbraking of the trailer. On the contrary, only that braking work is then performed by each part of the vehicle (tractor and trailer) which has to be applied due to the respective load of the individual parts of the vehicle.